The term "fiber" as used herein includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple). The term "yarn" as used herein means a continuous strand of fibers.
The terms "stain" and "staining" as used herein with reference to polyamide fibers means discoloration of such fibers caused by a chemical reaction thereof with a substance such as an acid dye.
Polyamide fibers are widely used in the home and industry as carpets, drapery material, upholstery and clothing. For instance, carpets made from polyamide fibers are a popular floor covering for residential and commercial applications. Such carpets are relatively inexpensive and have a desirable combination of qualities, such as durability, aesthetics, comfort, safety, warmth, and quietness. Furthermore, such carpets are available in a wide variety of colors, patterns, and textures.
Polyamides may be dyed with acid dyes by forming an ionic bond between the dyes and the protonated terminal amine groups (--NH.sub.3 +) (which are also known as the polyamide's "free amines" or "free amine end groups") present in the polyamide polymer chain. In certain instances, it is desirable to decrease the dyeability of polyamide fibers, especially nylon 6 fibers which contain a large number of acid dye sites. Such fibers have a reduced affinity for acid dyes. When such fibers are combined with polyamide fibers having a normal dyeability, and dyed, the resulting yarns have a two-tone effect. A representative procedure for reducing the dyeability of polyamide fibers is disclosed in U.S. Pat. No. 3,328,341, to Corbin et al. which is hereby incorporated by reference. Also of interest is British Patent No. 1,142,297 to Burrows.
Corbin et al. describes the use of butyrolactone to reduce the acid dye affinity of otherwise unmodified nylons. The suggested mechanism of action is by reduction of the number of amino end groups.
Although frequently polyamide fibers are anionically dyed, this is not always the case and there are a number of methods to render polyamides cationically dyeable. Some of the problems encountered when rendering polyamides cationically dyeable are ozone stability, shampoo fastness and cross staining. Perhaps the work described in U.S. Pat. No. 3,389,549 to David represents a leading work in this area. That patent discloses the copolymerization of, for example, 5-sulfoisophthalic acid with polyamide monomers, specifically , .epsilon.-caprolactam.
U.S. Pat. No. 3,846,507 to Thomm et al. describes a blend of polyamides having benzene sulfonate units and unmodified (normal) polyamides. The resulting polyamide has from 20 to 100 sulphonate gram equivalents per 10.sup.6 grams of total polyamide and from 35 to 80 amine gram equivalents per 10.sup.6 grams of total polyamide and a certain affinity for cationic dyes.
Polyamides modified with aromatic sulfonate units are taught to have improved acid-dye resistance in U.S. Pat. No. 4,579,762 to Ucci.
While nylon 6,6 containing 5-sulfoisophthalic acid carpet yarns have somewhat acceptable ozone and shampoo fastness, nylon 6 containing 5-sulfoisophthalic carpet yarns that have poor ozone and shampoo fastness, especially after autoclave or superba heat setting.
Allied Chemical Company has modified nylon 6 to contain lithium, magnesium or calcium salts of sulphonated polystyrene which results in nylon 6 copolymer carpet yarns with acceptable ozone and shampoo fastness. Several patents exemplary of the Allied work include, U.S. Pat. Nos. 3,898,200 and 4,097,546, both to Lofquist, and U.S. Pat. No. 4,083,893 to Lofquist et al. Yet, such yarns containing sulphonated polystyrene cross stain with acid dyes more than yarns which contain 5-sulphisophthalic acid.
Due to acid dyeability, polyamide fibers are severely and permanently stained when contacted with certain artificial and natural colorants present in common household beverages. Examples of such beverages include coffee, red wine and soft drinks. One of the commonly used acid-dye colorants used in beverages is FD&C Red Dye No. 40, which is also known as Color Index Food Red 17. When a beverage containing this dye contacts polyamide fibers, severe staining can result. As a result thereof, many carpets containing polyamide fibers such as nylon 6, nylon 66, and the like are replaced not because the carpet wears out, but because of staining.
In an attempt to alleviate the soiling and staining of carpets containing the polyamide fibers, polyamide fibers are sometimes treated with fluorochemicals for the purpose of reducing the tendency of soil adhering to the fibers of the carpet and to reduce wettability of the fibers. Although such a treatment offers some protection against soiling, the treatment affords little protection to the carpet from spills containing acid dye colorants unless the spills are immediately removed from the carpet, i.e., before the carpet has been wetted out with the stain.
Various compounds, sometimes referred to as stainblockers, including sulfonated aliphatic or aromatic compounds including sulfonated naphthol- or sulfonated phenol-formaldehyde condensation products have been applied to polyamide fibers in order to impart stain resistance to the fibers. Exemplary is U.S. Pat. No. 4,592,940 to Blyth et al. A problem associated with such products is that large amounts of these compounds must be utilized to achieve sufficient stain resistance in certain fibers.
Recently, yarn producers have begun incorporating colored pigments into nylon yarns to improve their resistance to degrading and fading in ultraviolet light, to give improved resistance to chemicals and noxious fumes and to give permanent coloration which is not removed by washing. Exemplary is European Patent Application No. 0 373 655 A2. However, when light shades of pigment are used, acid dye stains from accidental spills are visible on the surface of the filaments.
U.S. Pat. No. 4,374,641 to Burlone describes a color concentrate for pigmenting thermoplastic polymeric materials. A water soluble or dispersible polymer which may be sulphonated is used with a coloring agent which may be a pigment.
While some pigments can be mixed easily into the nylon without adversely affecting the filament spinning operation most pigments cause some difficulties while being mixed into the nylon or in subsequent spinning and drawing operations. In general, organic pigments crosslink nylon, raise its viscosity, form spherulites which weaken the fibers and cause increased draw tension and filament breaks. Many inorganic pigments depolymerize nylon, raise the number of amine ends (thereby increasing the susceptibility of the nylon to acid dye stains), lower the viscosity and also form spherulites. For example, pigments containing iron oxide or zinc ferrite and particularly a combination of the two give very poor operability. Either type of pigment in large particles weakens the fibers, clogs the spinning pack filters and causes breaks. On the other hand, very finely divided pigment agglomerates to form larger masses of varying size causing the same problems as large particles. Such masses also color the polymer unevenly and less effectively due to poor dispersion of the pigment in the polymer.
Patterned or multicolor carpets also can be made by mixing yarns which are not anionically dyeable with synthetic or natural yarns that are.
Thus, there remains a need for a carpet yarn which may be made from common nylon bases and yet has good ozone resistance and fastness to repeated shampooing, as well as resistance to staining by acid dyes.